The geology
of Nunavut records almost three-billion years of Earth history.
Our understanding of this history ranges from excellent in selected areas
that have undergone multi-disciplinary study in recent years, to rudimentary
in numerous vast tracts that were initially (and most recently!) investigated
in the Geological Survey of Canada's great helicopter reconnaissance operations
of the 1950's and 1960's.

For the
purposes of the present summary, Nunavut's geological history can be subdivided
into three main temporal blocks; the Archean, the Proterozoic and the Phanerozoic.
Each era is characterized by a distinctive suite of rocks, tectonic events
and resource endowment.

ARCHEAN

Rocks
of Archean age are exposed throughout Nunavut, and undoubtedly underlie
much of the territory that is covered by younger rocks. The Archean of
Nunavut is characterized by granite-greenstone
terranes, similar in most respects to Archean cratons globally. Nebulitic
migmatitic gneisses, that range from granodiorite
to quartz monzonite are among the oldest rocks in Nunavut and exposed in
parts of northern Baffin Island, the Melville Peninsula, and southwest
across the mainland. These rocks are complex and texturally diverse, ranging
from massive to finely foliated and thinly banded. Schlieren, lenses and
boudinaged bands of amphibolite, metasedimentary,
granitoid and rare ultramafic rocks are present. Discordant mafic sheets
that truncate early compositional layering in the rocks, but that are folded
and locally boudinaged, may represent dykes that predate younger supracrustal
rocks.

Late Archean
supracrustal rocks, consisting of ultramafic, mafic, intermediate and felsic
volcanic rocks, siliciclastic rocks and ironstones, comprise the greenstone
belts that host much of the gold and base metal
endowment of Nunavut. In the northern Slave craton of western Nunavut,
these rocks (Yellowknife Supergroup) host numerous deposits (e.g. Ulu,
George Lake, Boston, etc.) and the iron-formation
host rocks of the Lupin Au Mine. In
southern central Nunavut (western Churchill Province), similar rocks host
many deposits, including those at Victory Lake, Noomut, Heninga Lake, and
the Meliadine Au deposits. In the northern
part of the Churchill Province, ultramafic volcanic rocks, quartzite and
iron formation characterize the Woodhurn and Prince Albert groups; while
the former hosts the Meadowbank Au deposits,
the latter package of rocks is less well known hut appears to have significant
potential for Au mineralization. The
Canada-Nunavut Geoscience Office will launch a major new regional mapping
project in the southern Prince Albert Group (Committee Bay belt) this coming
summer. Rocks of the Prince Albert Group continue northeastward across
the Melville Peninsula and onto northern Baffin Island, where they are
represented by the Mary River Group. Some of the richest iron
deposits in the world, as well as elevated Au
potential, are found in these rocks.

Late plutonic
activity is in large part synchronous with, to slightly younger than, volcanism
in these greenstone belts, suggesting that there may be, in part, a genetic
relationship between the extrusive rocks and some of the intrusions. Monzogranite
to granodiorite plutonic rocks intrude both the greenstones and the older
orthogneisses. A phase of high-grade metamorphism is locally recorded at
—2.5 Ga across much of the Churchill Province.

PROTEROZOIC

Much of
the Churchill Province was covered by extensive siliciclastic deposits
in the earliest Proterozoic; this is recorded in the strata of the Hurwitz
Group and related successions. Younger siliciclastic and carbonate rocks
of the Penrhyn Group on the southern Melville Peninsula, and their along-strike
correlatives of the Piling Group (central Baffin Island) represent a continental
margin succession deposited on Archean crust. The stratigraphically lowest
strata consist of quartzite and feldspathic quarzite, and is overlain by
dolostone, marble and calcsilicate gneiss, with minor amounts of siliciclastic
rocks and as well as rare rusty schist and minor sulphide-facies iron
formation. Much of the upper part of the basin comprises a relatively homogeneous
succession of grey-weathering psammitic rocks that are volumetrically the
most important component of the Piling and Penrhyn groups. These rocks
have elevated potential for base metal and Au
mineralization; the Black Angel Mine, a past-producer of Zn
and Pb, is hosted in correlative carbonate rocks of the Karrat
Group on the coast of central West Greenland. On southern Baffin Island,
similar contemporaneous stratigraphy (the Lake Harbour Group) contains
ultramafic sills that have recently been investigated for their Ni potential.
In southernmost Nunavut, basal clastic rocks and overlying volcanic and
carbonate units are well exposed on the Belcher Islands in southern Hudson
Bay. These rocks record the subsidence and rifting of the western margin
of the Superior craton. Paleoproterozoic deformation, and a strong, attendant
thermal overprint are recognized throughout the map area. These Proterozoic
successions were deformed and metamorphosed during the Ca. 1.80
Ga Trans-Hudson Orogen, a period of global collisional and accretionary
orogenesis. In collaboration with the GSC (Ottawa), the Canada-Nunavut
Geoscience Office will launch a major new regional mapping project in the
Piling Group (central Baffin Island) this coming summer.

Renewed
rifting of the assembled continental mass is recorded in northern Baffin
and Bylot islands, where the Bylot Supergroup comprises > 6 km of non-metamorphosed
basal volcanic, siliciclastic and carbonate rocks. A system of northwest-trending
normal faults, some of which played a role in physically controlling the
deposition of the Bylot Supergroup, divides the Borden Peninsula into a
series of horsts, grabens, and half-grabens interpreted to record two phases
of ca. 1.27 Ga rifting and regional subsidence. Zinc
and lead ore of the Nanisivik Mine is hosted in carbonate strata
of the Bylot Supergroup. Up to 6000 m of correlative siliciclastic and
volcanic rocks (Fury and Hecla Group) unconformably overlie Archean and
Paleoproterozoic crystalline basement along the shores of Fury and Hecla
Strait It has been estimated that the Bylot Supergroup/ Fury and Hecla
Group may have been deposited over a period of ca. 75 million years. These
rocks were gently folded and faulted prior to deposition of the overlying
Phanerozoic strata.

Paleozoic
rocks cover approximately one-third of Nunavut. Strata lying to the west
and northwest of Fury and Hecla Strait are part of the Arctic Platform
that continues northward onto Ellesmere Island, whereas those to the southeast
underlie the Foxe Basin and represent the northern continuation of the
Hudson Platform.

The earliest
Cambrian strata, characterized by a thick clastic sequence, record the
initial subsidence and rifling of the craton. subsequent marine inundations
of the stable craton. From the Cambrian to the Silurian, thick carbonate
successions record stable platform conditions; these rocks have significant
potential for oil and gas reserves.
From the Late Silurian to Early Devonian, much of the Arctic Platform was
affected by

Caledonian
orogeny; uplift and erosion led to the deposition of a thick orogenic clastic
wedge, with elevated potential for red-bed type
Cu deposits. In the late Devonian, east-west compression (Ellesmerian
orogeny) may have been the driving force behind the Mississippi-Valley
type mineralizing event(s) that gave rise to the Zn-Pb
deposits of the Polaris district in the central Arctic archipelago. In
collaboration with the GSC (Calgary), the Canada-Nunavut Geoscience Office
will initiate a thematic investigation of the regional dynamics of the
Polaris Zn-Pb system(s) in the summer
of 2000.

From the
Carboniferous to the Cretaceous, renewed rifting led to the formation of
the Sverdrup Basin in northernmost Nunavut characterized by the deposition
of a thick clastic and carbonate succession. These strata host significant
reserves of gas and oil, including
the past-producing Bent Horn light crude
field. In the late Cretaceous to early Tertiary, renewed rifting led to
alkaline volcanism and the deposition of a succession of siliciclastic
rocks in northern Baffin Island, southwestern Bylot Island, as well as
northern Ellesmere Island. These rocks are remnants of a succession that
covered much of the Canadian Arctic archipelago, deposited as a consequence
of local uplift driven by a complex series of plate adjustments related
to the opening of Baffin Bay and the Labrador Sea. In northernmost Nunavut
the Eureakan orogeny is characterized by compression and strike slip faulting,
a consequence of the rotation of Greenland.

In eastern
Nunavut, a cluster of kimberlite pipes
is centered on Somerset Island, with exposures on the northern Brodeur
Peninsula and northwestern Baffin Island. Several of the Somerset Island
pipes are known to be diamondiferous; they were emplaced ca. 100 Ma. In
western Nunavut, diamondiferous pipes such as Jericho occur in the northern
continuation of the Lac des Gras field in the northern Slave Province.
Numerous other pipes have been identified on Victoria Island.

In conclusion,
the geology of Nunavut spans much of Earth history, and contains a wide
spectrum of economic commodity types. While Nunavut presently trails other
parts of Canada in the development of these resources, ongoing and new
investigations will advance our understanding of the territory.